Azeotropic distillation of xylenes



March 16, 1954 G. H. FoxoN 2,672,436

AzEoTRoPIc DISTILLATION oF xYLENEs Filed May 28, 1951 n uentor:

Attorneys.

Patented Mar. 16, 1954 AZEOTROPIC DISTILLATION OF XYLENES Gordon Howard Foxon, Norton-on-Tees, England, assigner to Imperial Chemical Industries Limited, a corporation of Great Britain Application May 28, 1951, Serial No. 228,559

Claims priority, application Great Britain June 14, 1950 7 claims. 1

This invention relates to a process for separating xylenes from mixtures such as petrol or cracked petrol fractions which contain them together with non-aromatic compounds of the parain, naphthene and olene type.

By xylenes in this specification we mean, in addition to ortho, meta, and para-xylene, also ethyl benzene and styrene.

It is already known to separate xylenes from associated non-aromatics by azeotropic distillation with 2methoxyethanol in the presence or absence of water. In the case of the use of 2- methoXy-ethanol in conjunction with water it has been proposed to effect the removal and recovery of the Z-methoxy ethanol for re-use by employing such a quantity of water that the overhead fraction consists substantially of ternary azeotropes between the non-aromatic compounds, Z-methoXy-ethanol and water, or such a quantity of water that separate zones, one containing Z-methoxy ethanol and nonaromatics, the other containing water and nonaromatics, are maintained in the distillation column.

According to our invention We separate xylenes of the kind hereinbefore defined from nonaromatic compounds of the paraffin and/or naphthene and/or olefine type present in hydrocarbon feedstock such as petrol or cracked petrol fractions by continuous azeotropic distillation of the feedstock with 2-methoxy ethanol containing a quantity of water insufficient both to allow two liquid phases to form in the distillation column itself and to form ternary azeotropes with all the non-aromatic compounds in the overhead fraction, but sufiicient to cause separation of the overhead fraction from said azeotropic distillation into twoliquid phases on cooling to such a temperature that the lower one of these two liquid phases contains most of the 2- n'iethoXy-ethanol together with most of the water,

the upper phase being rich in non-aromatic compounds, the xylenes being taken off in the bottom fraction from the main azeotropic distillation.

The lower phase is, according to a feature of the invention, preferably continuously recycled without any further treatment, by returning it to an intermediate point of the main column at or near the point at which the fresh hydro- I;-to the vesselin which the two layers form. 'The `liquid from the bottom of i this refractionating 2 column consists of substantially pure nonaromatic hydrocarbons.

In practice it has also been found desirable to operate the main azeotropic column in such a manner that the bottom fraction contains a few per cent of Z-methOXy-ethanol and to recover this material in a separate fractionating column, returning the overhead fraction from this column, which consists of the 2-methoxyethanol together with some xylenes, to an inter.- mediate point of the main azeotropic column at or near the point at which fresh hydrocarbon feed and recycle material are introduced. The liquid from the bottom of this refractionating column is then Xylene substantially free from 2- methoxy-ethanol.

The feedstock should preferably have a boiling range of 125-150 C., more preferably 13G-145 C.

The process is preferably carried out at substantially atmospheric pressure although if desired it may be carried out at either moderately reduced or moderately elevated pressures.

The quantity of water to be used in the process of our invention is limited on the one hand by the amount which causes phase separation in the main azeotropic column and on the other hand by the amount necessary to produce satisfactory phase separation of the condensed overheads in the decanter. In practice it has been found that our process may be conducted with the Z-methoXy-ethanol fed to the main azeotropic column containing approximately 1 to 9 per cent water. Preferably the 2methoxy ethanol fed to the main azeotropic column should contain about 3.5 per cent water.

The single ligure of the accompanying drawing illustrates diagrammatically and by way oi example, only, a system in which the present l in- Vention may be carried into effect.

In this figure, I is the main azeotropic distillation column with boiler heater 2 and'internal condenser 3. The feedstock enters at halfway up'the column. The overhead fraction is taken to condenser 5 cooled by cooling means 6 and thence through a further cooler 'I into a decanter 8 where it separates into two layers. The lo-wer layer is recycled to the entry point 4 of the feedstock into column I. The upper layer is stripped of 2methoxyethanol in column 9 heated by heating means IB and provided with internal condenser II; the non-aromatics leave the bottom ofcolumn 9 substantially free of 2-methoxyethanol. The overhead fraction from column 9, being an azeotropic mixture of 2methoxy ethanol and non-aromatics, is recycled to the decanter 8. The bottom fraction of column I is rich in the desired aromatics. .It is taken to a separate column I2 heated at I3 and with in'- 4tern'al condenser. I4 where azeotropic. mixtures yci'jfaromatics .and 'Z-methoz'cy-ethanol vdistll 

1. A PROCESS FOR SEPARATING AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF XYLENES, ETHYL BENZENE AND STYRENE FROM NON-AROMATIC COMPOUNDS WHICH COMPRISES CONTINUOUSLY AZEOTROPICALLY DISTILLING IN A COLUMN THE MIXTURE FROM WHICH SAID MEMBER IS TO BE SEPARATED, WITH THE ADDITION OF 2-METHOXY-ETHANOL AND OF AN AMOUNT OF WATER WHICH IS INSUFFICIENT BOTH TO ALLOW TWO LIQUID PHASES TO FORM IN SAID COLUMN AND TO FORM TERNARY AEOTROPES WITH ALL THE NON-AROMATIC COMPOUNDS WHICH DISTILL OFF IN THE OVERHEAD FRACTION IN SAID COLUMN BUT WHICH IS SUFFICIENT TO CUASE SEPARATION OF SAID OVERHEAD FRACTION INTO TWO LIQUID PHASES ON COOLING TO A TEMPERATURE WHICH CAUSES THE LOWER ONE OF SAID TWO LIQUID PHASE TO CONTAIN MOST OF THE 2-METHOXY ETHANOL TOGETHER WITH MOST OF THE WATER AND THE UPPER ONE OF SAID LIQUID PHASES TO BE RICH IN NON-AROMATIC COMPOUNDS, SAID ADDITION OF 2-METHOXY-ETHANOL CONTAINING FROM 1 TO 9% OF ITS OWN WEIGHT OF WATER, THE VOLUME RATIO OF 2-METHOXY-ETHANOL TO NON-AROMATIC HYDROCARBONS IN THE MIXTURE FROM WHICH SAID MEMBER IS TO BE SEPARATED BEING FROM ABOUT .9 TO ABOUT 1.35:1, COOLING SAID OVERHEAD FRACTION TO CAUSE IT TO SEPARATE INTO THE AFORESAID TWO LIQUID PHASES TAKING OFF THE MEMBERS OF SAID GROUP IN THE BOTTOM FRACTION FROM SAID COLUMN AND CONTINUOUSLY RECYCLING, WITHOUT ANY FURTHER TREATMENT, SAID LOWER PHASE TO SAID COLUMN TO ACT AS SAID ADDITION OF 2-METHOXY-ETHANOL AND WATER. 